The present invention relates to a dielectric film capacitor and a method of manufacturing the same.
An increase in speed and capacity and a reduction in size will be more and more demanded for devices (e.g. mobile communication terminals represented by portable telephones) in the information technology field. Accordingly, high-performance devices have been widely and extensively researched and developed in order to satisfy such demands. A dielectric material having an ABOx (perovskite) crystal structure represented by barium titanate, barium strontium titanate, or lead zirconate titanate has been widely used in the electronic device field as the material for a capacitor, memory, and the like.
In order to further reduce the size and increase the performance of such electronic devices, it is indispensable to reduce the thickness of each element. This requires establishment of manufacturing technology for a dielectric film capacitor exhibiting high performance and high quality.
A dielectric film capacitor generally has a structure in which a substrate, insulating layer, lower electrode, dielectric film, and upper electrode are stacked in that order. The dielectric film may be formed by sputtering, chemical vapor deposition (CVD), molecular beam epitaxy (MBE), a sol-gel method, metalorganic decomposition (MOD), or the like. In particular, a liquid phase method has attracted attention which reduces production cost, facilitates composition control, easily provides a desired shape, and does not require an expensive manufacturing device.
When forming the dielectric film using a vapor phase method, the dielectric characteristics of the dielectric film must be generally improved by subjecting the resulting dielectric film to heat treatment in an oxidizing atmosphere. When forming the dielectric film using a liquid phase method, a coating obtained by applying a sol-gel solution in which an organic compound as the raw material for the dielectric film is dissolved in an organic solvent or a solution in which dielectric material particles are dispersed must be generally subjected to heat treatment in an oxidizing atmosphere. Therefore, a noble metal which is rarely oxidized is used as the material for the lower electrode. Specifically, a material containing platinum (Pt) is widely used as the material for the lower electrode.
When forming a dielectric film capacitor on a silicon wafer, a lower electrode (e.g. Pt film) is formed on a silicon-based insulating layer (e.g. silicon oxide layer) formed on the silicon wafer, for example. However, since the adhesion between the silicon-based insulating layer and the lower electrode (Pt film) is poor, the lower electrode is easily separated from the silicon-based insulating layer. The separation of the lower electrode makes it difficult to manufacture a dielectric film capacitor using a method such as patterning or dicing/cutting. In order to solve this problem, a method has been proposed in which an adhesive layer is formed between the silicon-based insulating layer and the lower electrode in an attempt to improve the adhesion between the silicon-based insulating layer and the lower electrode.
For example, JP-A-8-78636 attempts to improve the adhesion between a silicon oxide layer and a noble metal electrode film by forming a titanium (Ti) film (adhesive layer) between the silicon oxide layer and the noble metal electrode film. On the other hand, the substrate may be warped due to oxidation of the Ti film, or an oxide resulting from oxidation of the Ti film may be diffused at the interface between the noble metal electrode film and the dielectric film.
JP-A-2004-349394 attempts to improve the adhesion between a silicon oxide layer and a platinum electrode film by forming a gold (Au) film (adhesive layer) between the silicon oxide layer and the platinum electrode film, for example. However, it is disadvantageous to form a multilayer noble metal thin film from the viewpoint of device manufacturing cost. Moreover, this method does not necessarily provide improved adhesion due to insufficient adhesion between the Au film and the silicon oxide layer.
JP-A-2005-85812 and JP-A-2005-101531 attempt to improve the adhesion between a silicon oxide layer and a platinum electrode film by forming an adhesive layer using the same material as the dielectric film between the silicon oxide layer and the platinum electrode film to reduce the stress applied to the film, for example. According to this method, since the adhesive layer and the dielectric layer are formed of the same material, the characteristics of the dielectric film capacitor do not deteriorate even if the adhesive layer is diffused at the interface between the lower electrode and the dielectric film. However, since it is necessary to select a dielectric material which can function as the adhesive layer, the material composition which may be used for the dielectric film is limited, whereby the characteristics of the dielectric film capacitor may be impaired.